Research On Technology And Key Components Of Punching And Filling Sand In Coastal Saline Soil

Soil salinization has been considered as a prominent problem of ecological environment in arid and semi-arid agricultural region.The salinization results in viscous soil structure,slow air permeability,and strong capillary action,which leads to crops' physiological drought,and has negative effect on crop growth.The engineering method is one of the typical measures on soil salinization improvement,which has been verified to enhance irrigation leaching and reduce the accumulation of salt in the soil surface.However,this engineering method also has its shortages such as heavy workload,high cost,difficulty of large-scale applications,etc.Therefore,aiming at the great salt content,viscous soil structure,and slow air permeability of coastal salinization soil,a punching and filling sand(PFS)method was proposed,and the matched PFS equipment applied in coastal salinization soil was studied.The main results and conclusions are as follows:(1)The irrigation experiments were carried out in coastal salinization soil region of Tianjin,and soil moisture and salt content were measured to analyze the effect of PFS method on soil water and salt transport.Experimental results indicated that 10 cm or more punching depth treatments of PFS method increased total desalinization by 50.7%to 176.5%in 0-30 cm soil layer,as compared to the unpunched treatment.In addition,considering the local agronomic standard,10 cm punching depth and 30 holes/m2 punching density were recommended as an adaptable PFS project.(2)Aiming at the mechanical properties of coastal salinization soil,the mechanical model of punching component was established whish depended on the soil shock theory and limit equilibrium theory.The mechanical model showed that soil density,cohesion,friction angle,configuration parameters of punching component,and the punching velocity were the key factors that affect punching capacity.The head type of aerating part was determined as inner concave arc through numerical analysis and multi-objective programming,and its cone angle was 450 and the apex tangent angle of inner concave arc was 320.Based on the impact load model of the aerating part,the model of aerating critical kinetic energy which was impacted by saline-alkaline soil was established.It was found that the needed kinetic energy was increased with the increase of aerating depth,while it was decreased with the increase of aerating part's weight under the same aerating depth.The field impact test of saline-alkaline soil further validated the feasibility of the critical kinetic energy model.(3)According to the demand of high precision,the problems of high impact and easy wear and the shortage of high dependence on working speed of the existing vertical punching device,a flexible passive five-bar punching mechanism was designed.Based on the establishment of kinematics model of five-bar punching mechanism,the constraint condition for key parts was analyzed.Combined with the analysis of working principles and motion characteristics,the structure parameters of punching parts were determined.Based on simulated annealing optimization algorithm,mechanism parameters was optimized:length of frame AB,crank AC,long rod CE,connecting rod ED,support arm BD,punching needle EP was 420 mm,75mm,630mm,270 mm,224mm,150 mm,respectively;angle of frame AB was 111°,and the initial angular displacement of support arm BD was 280°.Meanwhile,computer simulation of punching process showed that the optimized structure under best unit advance speed reduced the inclination angle by 24%,and when the working speed was 3?4.7 km/h,the inclination angle was less than 4.6?,which satisfied design requirement.(4)The working process of passive device was analyzed,and the matching conditions of return spring were researched by the kinetic study of support arm.Combining with the soil mechanical properties of the study area,the equipping standard of return spring was summarized:more than 14 cm of the effective compression amount,and less than 370 N of the maximum compressive stress.Based on the tilt character of punching needle during punching process,the working principle of sand transportation of side opening type punching needle was researched.By response surface methodology,the structural parameters of side opening type punching needle were optimized,and the optimum parameters are as follows:the depth of side opening was 7.27 mm,the height of side opening was 41.67 mm,and the width of head section was 12.70 mm.Through the designing of machine driving,passive device and sand transportation device,the PFS prototype was formed and the field test was carried out.The experiments of punching effects verified the veracity and rationality of flexible passive five-bar punching mechanism.When the forward velocity of prototype was 3?5 km/h,the PFS density was 25?41 holes/m2,the punching depth was uniform with the variable coefficient less than 6%,and the average inclined angle of holes were ranged from 1.6°?3.4°.The experiments of filling sand effects showed that the average proportion of sand filling ratio of the PFS prototype was 77.1%,which can basically complete the sand filling process.Meanwhile,the capacity of filling sand needs to be improved.